Radio direction finding system



Sept. 4, 1945q w. P. LEAR RADIO DIRECTION FINDING sYsTEN 1940 5 Sheets-Sheet 1 Filed March 1,

Sept. 4, 1945. w. P. LEAR RADIO DIRECTION FINDING SYSTEM Filed March 1, 1940 3 SheetS-Sheet 2 N OPOE lOOq OF :urzsm 1332 ,N www EN I ATTORN EY.

Sept 4 l94f5 w. P. LEAR RADIO DIRECTION FINDING SYSTEM 3 Sheets-Sheet 3 INVENTOR. 5. @var 0 w m m n l M A ra- IQI., llllr'l R l WH H Jw as w 2 2 m p. 0 N R m 9 Z/ .w o m M Y 2 P u o 50.6 T 70 E U lllll -112... R. A 3 LT i 2 G mp, mn. ..A m

AI c lr .s .NA .4.

Awilliam ATTORNEY.

Patented Sept. 4, 1945 ATEN-T `ori-fici:

VvRADIO DIRECTION FINDING SYSTEM` William P. Lear, Chicago, Ill., assigner, by mesne assignments, to Lear, i Ohio, a corporation of Illinois Application March 1, 1940, Serial No.' 321,623

12 Claims. (Cl. 250-11) This invention relates to radio direction finding systems vand morev particularly' relates to novel switching arrangements `for automatic direction finder circuits. This case is a continuation-inpart of my Patent No. 2,308,521 issuedon January 19, 1943, entitled Automatic radio direction indicator.

In accordance with the present invention, I provide `simple, switching arrangements for readily converting an automatic unidirectional indication system either to manual directional reception, or to non-directional reception for communication or radio range navigation, or to automatic -bi-directional indication during excess static reception conditions. Severe static conditions at times encountered in night, sometimes renders automatic directional indications indenite; .or if denite, renders corresponding aural reception unintelligible. For such conditions I provide an auxiliary directional antenna for the automatic directional system connectible with the usual directional antenna, and arranged to give accurateV in-line, directional indications during even severe static reception, as well as give intelligible voice reception. Such directional `indication, however, is bi-directional in nature, be-v ,present invention is illustrated inconnection with the unidirectional 360. automatic direction finder system and .circuits disclosed in the parent case Patent No. 2,308,521 referred to above. Two loop antennae are employed for the loi-directional circuit, both antennae being physically coupled together. .The lui-directional indications are accurate in'degrees'buthave reciprocal ambiguity. The pilot, however, can ascertain his relative 180 position withrespect tovhis heading and to the directional bearing indicated, and is thus in a position toresolve 'the 180 ambiguity of the bi-directional indications.Y One method of resolving the 180 position is to switch the system to unidirectional operation and check the quadrant of the unidirectional bearing. Another is to maneuver thev aircraft off-course for check bearings, or to rely'ion other navigationaldevices on the plane.

It is accordingly an object vof 'my present invention to provide novel multi-circuit switching arrangements for radio direction finder systems.

Another-object of my present invention is to provide a novel switching arrangement for a direction nder system, capableof readily converting the system into anyone of several distinct modes of operation. f

Still another object of my present invention is tofprovide a novel automatic direction finder sys- Incorporated, Piqua,

tem giving accurate in-line" bearing indications during severe static conditions. y

A further object of my present invention is to provide a novel radio direction finder system having circuit arrangements for ready conversion from unidirectional operation to bi-directional operation for static reception conditions. n

These and further objects of my present invention will become apparent in the following description of preferred embodiments of the invention, illustrated in the drawings, in which:

Fig. 1 is a diagrammatic representation of a complete automatic direction finder system to which my present invention is applicable.

Fig. 2 is a schematic circuit diagram of the direction iinder system of Fig. 1, illustrating a switching -arrangement for altering its mode of operation.

Fig. 3 is an electrical diagram of part of the radio directional system of Fig. 2, incorporating an auxiliary directional antenna in circuit with switching means for converting the system to bidirectional reception.

Fig. 4 is a partial diagrammatic representation of a modified arrangement of the Ibi-directional conversion system of Fig. 3.

Fig. 1 is an electrical blockl diagram illustrating the coaction of the components entering into the automatic direction finder. A coil wound directional or loop antenna I0 is mounted at the end of rotatable shaft II, and arranged for free rotation in either directionfover the full 360 degrees of arc. The leads of loop antenna. 10 terminate in slip rings I2 coacting with brushes I3 for electrical connection thereto. Low' impedance cable I4 electrically connects brush I3 to the primary Winding of the loop signal radio frequency transformer I5. Loop antenna VIll is preferably designed with a relatively low impedance or number of turns in order to efficiently receive signal energy over a Wide frequency range and transmit the received radio Ysignals to remotely situated radio frequency tuning units. Loop antenna I0 is mounted outside of the aircraft for most efficient signal pick-up, preferably on top of the fuselage to minimize thepossibility of mechanical injury. A streamline housing indicated in dotted lines at I6 may be used .to protect the loop antenna from Wind currents and externalinjury, and to minimize its aerodynamic resistance.`

A variable condenser I6, in shunt with the secondary of radio transformer I5, is used to tune-in the desired radio station. -The'magnitude of the tuned-in radio signal impressed upon the input of the loop radio frequency amplifier II depends upon the angular position of the loop antenna I0 with respect to the direction of the oncoming radio waves.r When the loop antenna is in its null position, with yits plane perpendicular to the direcl tion of the oncoming radio waves, no signal is imort-:left of `the null position o f loop antenna I position,. son that ythel proper ccunter-rotation of motor 310:Wil1 Yoccur to bringthe loop Yantenna to thenll signal position. Gearing 56, shownas beveled gears, may be a worm and worm gear drive, andV preferably has a high reduction ratio.

ARelayl Iremains energized until loopantenna ID is rotatdto'reach its null position, .whereupon'tle control signal derived from theloop signal impressed uponampliler I'l is so reduced in value or obliterated( as'to cause relayl armature.,

53thA `drop back to itsneutral or back contact'posif tirgdeenrgizing andstoppingmotor 3U. Electrn'agnetic clutch 5 1 is electrically shunted across"thefmotoii'energization circuit to immediatly disconnect the motor from the loop an tenna, insuring a rapid stop of the loop rotation at'fthe timeA ofv inotcr deenergization, and elimihating the possibilityo'f overshootingor overdriving by the motor due to its mechanicalinertia.V 'Th'e frictionalforces yof gearing 5 6 and the bearings oftheloop are generally suiicient toluicklyfstop the loop rotation. An Aelectromagnetic brake mayfbe connected for braking the loop vupon motor deenergization. The high.

reductionfgearing ratio Vat56 minimizes possible overshnotingv of the loop, since one revolution of the motor causes only a small fractional degree of angularc rotation of the loop.

In practice I have constructed systems in accordance v'vith the present invention which automatically operate the loop and therefore the bearing indicator at arate of. 180 and more per second. The accuracy of the resultant bearing..

may readily b e madewithin ,1 of arc, i, e. the

actual directional indicationon the radiostation being correct to within 1 or less. The `bearing indications are on a 3 60" dial and move tothestationary vbearing position through theshorter angular path.

When loop antenna I0 reaches, or is substan tially at, its null signal position azero or substantially zero radio frequency signal is .im-

pressed upon radio frequency amplifierdl for modulation at 32 by the generated tonesignal.

from 3l. The magnitude of the control signal from amplifier 40 accordingly is also Zero, or substantially zero at that time, and control relays 50"`are Yin the deenergized position shown. The

loop accordingly 4remains stationary When it is at its electrical signal. null position with respect to the direction of the oncomingwaves. rIThis position corresponds to the geometric position.Y of theloop where the vplane of the openfface Y thereofiis'perpendicular to VVthe direction ci the onc'oniinf.;Y radio Waves. @Should the aircraft c arryingfthe loop antenna deviate from this direc? tion vtheloop will be energized bythe radio signaland impress it upon amplifier Il with a magnitude and "phase relation corresponding. tothe altered direction thereof. should the'defieetion of thejaircraft cause the lloop to receive asignal of' phase vcorresponding to that which energizes solenoid}5|, 'the above described `operatien of motor 3l) isrepeatedto bring the loon'to .the new null signal position; Should, however.. the

aircraft turn so thatloop` I0 is deviatedl in the,

opposite angular direction, the phase of the vconi trol signaleimpressed upon relay control tube system 45 Awill lbe ,different by .1809 and energize solenoid: 52 instead.` v

When solenoid 5 2 is energized, itsarmature 58; isattracted to front contact 59 to electricallyY completethe motor 30 circuit including clutch 51, ground, and battery 55. Electro-magnetic clutch 51 isfthereupon immediately engaged and -motor 3 0 .is rotatedin thedirection oppositetonthat` corresponding to its energization by solenoidl.. Motor isa reversible onein the `present case,4

andis not necessarily a direct currenttype. -Relayarmatures53- and 58 are arrangedso thatl the. direction of; current ovf throughfmotor '30.

is selectively reversed to cause motor 30 to rotate loopA l0 towards its null signal position in the shorter path of rotation. Thus,when solenoid 52 is. energized, motor 30 will rotatein a direction opposite to that dueto energization of relay 5I. Clutch 5l becomes engaged and loop antenna I0 isrotated to itsnull position in a direction oppor.,

site to that whenjrelay v5l -isv energized,v which direction isthe shorter path of rotation since the signal results yfrom an from nu11..

An indicator: is pointingloutits;direction andgives a true reading-ofthe bearing on a radio station'. Theloop antenna is generally placed remote from 4the cockpit.; A telemetering arrangement is .con-

. nectcd to theloop antenna and .av remote 360 de,-v

gree indicator is provided to; show the pilot the exact angular position of the loop at any time.`

The metering system `diagrammatically shown in Fig 1v comprises a loop position. transmitter 60 mechanically secured, to loop: shaft. Il.

transmitter 6 9; is energized by direct current source 6I andisioonnected by three-Wire cable 52.- to remote loop position indicatorl 64. mounted inthev lcockpit adjacent the pilot. Pointeri' "of indicator 6'4 moves in exact correspondence with loop antenna l0, and is arranged to point tothe center zero positi0n166 shown on the dial, when the axis o f loop I0 is parallelV to :the axisv of the` aircraft, i. e. when theiopen planev of the loop is perpendicular to Y ther direction of 4flight .of the aircraft. Y

When pointer (5isI at its ,center yzeropositicn shown, the direction ofthe oncoming radioA waves",

as received by the system is directly in line with the aircraft, the position of the radio station corresponding to the center. zero reading being directly ahead or on-course with respect to the'- direction of night. When the aircraft deviatesI from oncourse Aand flies toward the left of the transmitter station, the loop antenna will re' ceive a radio signal .which causes the generation of a control signal to operate either of control relays .5| or 52 to immediately return the lloopantenna'to Athe null position with respect to the direction towards thetransmitter station. In-

dicator needle. 65 accordingly is moved toy continuously point towards the fixed ground station.

A deviationv of ilighttowards the left of the station will cause vthe needle to deect towards the right orz'ero point by an equal number of, degrees orare.4 For example., should the aircraft.y de llect 10. degrees-off-course the needle 65 will? opposite loop deflection securedlto theloop antenna forv A direct` current Selsyn; type` telemetering system is. suit-A ableforthis purpose, and is described .in more detail in theparent application. '.Loop position immediately rotate'. i'degrees towidi the and the pilot. willi iumiedateyfibe of his new course:'withL respect; totl-'ie1acli'ei @Senter` were Wcorrespondsl tel the directielidi or the course: of" mghitfam the oil?V needle-66 corresponclsto the ectual direction toi the radio station with respect flight, .Con-irersielyf;- should the deflect his alrcmttzflilr. degrees towards the-'rightot they dinectiomt'o radio station, needle 6F- willi deflect I0: degrees towurds the` left'. thus. neecl= 'merely remember ttiatg. needle: GSi exactly points-ont"- tle= actue positionof the-radio groundv He maneuvers' arcrwtt t@ adj'ust his angular direction of 'Hight with respect directontu thevradio The accuracy of? indication is independent of the position of" indicator 6E 'since any residing thereof4 corresponds to auf' electcaknullspositiorr of the loop; andi no bol'-h ancing of; electrical-parameters: orsgnall com pnnents are required; tof mvniintxsinl the readings; Iii isthus possible tlie pilot' tol-Ey' at anyde Y sited; with respects to'y dradio stationi merely 4marin-taining` indicator needle W at' tha'tangular position on dial. Y

Ai manuel'loon rotatmrfswitchi t0 'is provides?r permit the pilot tu rotate the loew independently of the automatic direction finder contreir.-lv whenvthe equipment usent s manualf directimy miden ou' when mimi receistl'on is desti-e5 en the. 1oaop= alone during staticV conditions (which operationmayr be eeeted' by. thelselectior switch@ ing armligamenty msnm inFig.- 2)?, the-pilotoperates button 'H oit' theromtorfswltchfbr dfi-'wgaies-ri* actanee; and Vaids the eflicient' tuning" and I f ception ofthe radio signals' by theloop A transmission cable having ar capacitance Gf- Y about seo miero-mrcrofaracsfis mmeforiuse tion contralor the'loop position.` Wherebutteryh Lt .is pressed towards the: right; mature 'Fit thereot is counectedlto groundtllmugl contact* M together.' with clutch if is ener frombattery 55 to cause-loop Wto rotate in. a; corresponding Similarly,

buttonll is pushed towards the lett,- mdarmu A time:A Ik. thereof connected te ground through' Contact; 1 5,. the motor is madefto rotate; loop:l Wi iinL the opposite directibng. independently of. the op eration; at the autom-tiodirection' vmiden'circuit;

. Figs 2tfix= aischematlc electrical? circuit diagrama partially in; block: toms, illustrating elctrica/lf detailsot featurescompristngfr w prises-- ti'cal': automatic Ydireetmxtl- -nelr system con structedinzaccordancefw-th the pni'n'ciples et? my present nventinnz.'. Nmu-dix=ectionl is connected. to; primary-winding! I ofthe mummia,v is. use@ wim been aises-sanmartin groundif S:artisf-axst'oryfV directional recimtiorr` ist:

feasible overv a radio irequencyrange: as inw" as 186" kilo'cyclesi uprto- 2800 kilocycl'es a' single-loopl antenna; of about 20 mfc'rohenri'es inclwcton'ce.Y Y'The loopaairtenna;L will' have' 2U ohm: innocui@snoeii aft the lower frequency',A and a 499s ohm impemince:v at! the higher frequ'ericyiv Loop cableZ N has 'az capacitive re withthe ZOmicrohem-l'es loop antenna; amiens-- neet-s the loop antenne tothe input` ofl'oep ampiiner stage ME Duetolthe'lowimpedance'of the loop andv proportiormllyf low capacityl cablen Ff, it is possibletnruse an; e'lrceptionarllyl'ongljloori4 cable without serious'transmissm loss.

Signalsfror'ir rottetble` lbopV avntem'na.`v N are picked .off irovx'nh slip rings liby brushes Il electrically: connected tothe primury of radio'i 'equencytranstormer l through transmission: cable W. Radio f'l'ex'iuex'lcxrn transformer f8 is prefererbiy of the highlyembient and electrically" shieldedtype'.. A' powdered rorr coremay' be used" forthe radio frequencytransformers-ot" the system aswell ais for the intermediate frequency transformers:

The secondary winding of loop transformer 'H is shunted byturnii'igV condenser ft The of loop transformer' I1! is` connected to the con-l trol' grid electrode of radio frequency ampller pentod'e 82' forfurther' amplification 'andflntx'tti ductionl to the control grids of blancec muuu,"

lato'r stage. gezin oflb'opam'pllier Ilfisj manually controilabie-rheostat 83* co'nnectinrV thecaztlicfdev thereof to g'i-ound` The amplier' 8'?? is energized through" a' shunt radio? frequencyv chokel coili Sii connected tot the E supply; output olbopt ampliflerin" is pledftethe vcontrolvgriils ofl tubes N, Il" of' modul'atorI 3'2 throughu coupling condlsnsersv 81",81'. The cathodes of= tubeSi-BBV' SY are tied tngegtfef'A andfconnectedV to4 ground through ltr-pass con*- denser' w andi aA biasing* resistance t?, 90; 5icontrolled` by' seiector lill dscribeeb mr audio" frequency oscill'a'lor-Y Si"` comprising twotriades' 92, Brisarra'nged `'to` generate an audioortone frequency current cfu relatively lowfvffrequency: The control*` ofL triode's,` SPare'coup'l'ed tor-the anodes by condensers Si; Catholics of the'V ascii"-V` i lator'triod'es; are'- tiied together andi/connectablf'tbj' Y ground throughk blatsitrgy resistor 94";

(Dscillaltorl 3P is normally-i operative circuit of biasing' resistor' -94 is' completed' to4 ground?. Aiground connectlorrtherefr kwher-1 selector switch MfisI ini f; M

automatic direction` indicator operation.

su is; normally' mecliani'ciniyv` bia-seri away ri'oim contact By mmm'urlfvV pressihk' blade 99 im example Si?, againsucontact o'scnlutorvcir-j cuite 31 is compieted@ and aiJ tienev signal tegens. erat'ed for automatic" looprotation' control operffj` ation. Thus, the-punt caueft'ect automatic'xmll operation during: "loop only" receptim'r,. with bi1 directional ambiguityresuitingfin this case. 'The BT Supply ihr' the' anodes of oscilfator tllole'sl'n." is' arranged through ai' center-t'umzveciv mductance* 96!` connectedltuthe supply'throuxrr A and' resistance 99 are `sit'untedl acrossindactance colit and'timetheirpredete'r`l mine the frequeirxvcxf.v generated by'oscillator411':v Resistors; N1' amel'il m arec'cupled betweeitltlel grid electrodes of"- trici-lesl 92', andround. Intermediate tapes' F03. and' mf on'..respect irtU oscillatorl" to the grids ofxuodul'toi"V triodes if,

-86Uthrough coupling resistances |05, |06, of about lone megohm each and through coupling condenser |01, |01. Further resistances |08 and |09 normally connec'tfgrid coupling resistere |05 and |06 to ground to stabilize the grid circuits thereof. Control grid electrodes of modulator triodes 86, 186"simultaneously receive the audio frequency tone signal from oscillator 3| and the radio frequency signal picked up by directional antenna l0. y The electrical interaction of the respective signals 'is' described in connection with Fig. 3 of the parent patent. The output of modulator stage-32, obtained through the anodes of tubes 86, 86 is connected to opposite sides of radio frequency winding-33 coupled to secondary winding 24 of the non-directional antenna circuit. The anode'supply for modulator tubes 86. 86 is obtained through a center tap on winding 33 connected to the common B supply as indicated. The frequency of the loop modulated signals is the sum and difference of the received radio signals and the low frequency oscillator tone signal. The `simultaneous induction of the non-directional lradio frequency signals with the tone modulated loop signals upon winding 24, produces a resultant signal upon control grid H of radio frequency amplifier 80. The non-directional signal from antenna 20 serves as a reference signal or sense determinator, so that the right or left sense of the loop vantenna'signals is established for further control action on the loop antenna. Thus proper functioning of the automatic directional system is assured, bringing the loop antenna back to its null signal position tol give accurate indications. o e Y' The signals impressed upon the control grid of l'radio-frequency'pentode 80 are amplified and transmitted through output radio frequency transformer having its secondary winding tuned to resonance by variable condenser H2 shunted there-across. The output of transformer IH` is coupled to intermediate grid electrode H of the radio frequency mixer stage |20 through coupling condenser H6. Radio frequency mixer "|20 is shown as a heXode wherein grid electrode |1 adjacent to the cathode is energized by a signal emanating from a local beat frequency oscillator |2| operated in the usual manner for superheterodyne reception. The showing of beat frequency oscillator-i 2| in block diagram form is believed sufkcient, it being understood that the beating frequency is controlled by a unitary tuning( means connected with the variable tuning condensers of the radio frequency circuits. The anode and screen grid operating potential is supplied through respective resistors |22, |23.

The output of radio frequency mixer stage 20 comprises primary winding |25 of astep-down intermediate frequency transformer shunted by ,adjustable condenser |21 for resonatingfthe coil atrrthe intermediate frequency, such as455 kilocycles. fTransformer |25, |26 is a step-down transformer sothat a long low impedance transiriissionline |35' may be used to permit placing theintermediate frequency and audio frequency amplifier equipment remote from the radio frequency section including the directional and nondirectional radio signal amplifiers, and the loop modulator stage. -This arrangementalso makes it feasible to utilize the radio frequency and intermediate frequency sections with much higher gain than with the conventional combined type 'of construction. Transmission cable |30 is an electrically shielded low impedance cable, which coupling condenser 48.

'may-'well-.be 12 feet inlen'gth, terminating in a correspondingly low impedance primary winding |3| of step-up intermediate frequency transform- Secondarywinding |32 of the terminating transformer is shunted by a resonating adjustable condenser |33 to tune the transformer tothe intermediate frequency used. l

The output of step-up intermediate frequency transformer |3|, |32 is connected to the grid electrode indicated at |34 of the input stage of two-stage-intermediate frequency amplifier |35 shown in block diagram. The anode indicated at |316 of output stage of intermediate frequency amplifier |35 is connected to transformer |31, the primary and secondary windings of which are respectively shunted -by adjustable condensers |38 and |39 and tuned tothe intermediate frequency. An audio frequency detector stage |40 has its control grid. |4| connected to the output of intermediate frequency'transformer |31 for demodulating thesignals and producing corresponding audio frequency currents across cathode resistor |45 connected to ground. Both the radio signal modulations as well as the tone or control signal, if present, produce thev corresponding audio frequency signal across resistor |45 by the detector action. The anode of `detector |40 is connected to the common B supply as indicated. Condenser l46, between the cathode of detector |40 and ground, by-passes the higher order frequency currents from the audio frequency path. Y

The audio frequency signals are coupled to audio frequency pentode amplifier stage |50 by The anode circuit of amplifier |50 comprises resistance |5| connected to the common B supply and is coupled to the control grid |52 of a second audio frequency amplifier stage |55 through coupling condenser |53. Second audio frequency amplifier stage |55 is resistance-capacity coupled by anode resistor |156 and coupling condenser |51 to a further twostage audio frequency amplifier |60. It is to be understood that both the original audio fre- 'quencyfsignal modulations and the control or tone signal amplified together therewith, are impressed upon two stage amplifier |60 for further amplification to an appreciable signal level. The Youtput of amplifier |66v is coupled tothe aural amplifier indicated at |10, to the output of which earphones |15 are connected. The pilot adjusts the aural level of the signals by a separate manual control in aural unit |16. The output of audio frequency amplifier |60 is also coupled to further amplifier stages and |90 for selecting and further amplifying the control signal and impressing it upon relay control system 45.

The output of audio frequency amplifier |66 -is coupled to the control grid of amplifier stage |86 Yby coupling condenser |6| and phase shifting network |62, |63. Resistor |65 is shunted across phase shifting network |62, |63 connecting the control grid of stage |30 to ground. The relative impedances of resistor |62'and condenser |63 "are chosen to suitably shift the phase of the control signalY to be impressed yupon control grid |8| lto compensate for any misphasing thereof caused in the circuits prior to that point. Such phasing is made to cause the phase relation of the signal arriving at the input of tube relay control system #i5 to be substantially in-phase or 180 degrees cut-of-phase with the correspondingly impressed tone signal from amplifier 43.

Phase shifter network |62, |63 may assume other forms than the simple one shown, or be positioned at`r another part of the circuit. In

1a.. Contact 250, connected directly to non-directional antenna 20 through lead 25|, short circuits the non-directional signals and renders `them ineffective. At the same time the cathode circuit of oscillator tubes 92, 92' are ungrounded y Vsince blade a. is removed from contact 253. No tone signal is then impressed upon modulator vstage 22. 4Should the pilot desire automatic rotation of the loop to null, he presses switch 95 against contact 96 completing the cathode circuit to ground.

A n'ull indication in the loop only position is bi-directional, but useful when precipitation static conditions are encountered in flight. By turning the loop near its maximum signal reception. position, communication reception is feasible.' By viewing meter 240 the pilot can ob-l tain reliable directional determinations by the minimum or maximum signal strength positions. Biasing resistor 5| remains shorted to ground .throughswitch blade b and contact 250. Grid resistor |09 of modulator tube 86' is disconnected from ground and connected to an intermediate biasing potential at resistors 89 and 90 through 'contact 26|. Such connection of resistor |09 de- -creases the negative bias between the grid and `cathode Vof tube 86. Section 86 of modulator 32: isaccordingly rendered more sensitive for fsignal amplification than tube 86 which normally is biased near cut-oft. The loop signals are accordingly amplified through section 86 and impressed upon radio frequency amplifler stage 80 vby coupling coil 33 and through the remainder of the system. 1

With selector switch |00 in position 2, non- `directional antenna 20 normally impresses radio signals-upon the system, switch blades a and b lbeing connected to intermediate contacts 252 and 262 respectively. Resistor 9| is unshorted and is Aeffective in substantially increasing the biasing :voltage upon modulator stages 86, 86'. The total value ofthe resistance placed in the cathode to Yground circuit for modulator 32 is designed to be sufficiently large to over bias the modulator tubes 96, 86 and prevent the passage of loop radio signals or any tone frequency. Cathode resistor 94V of oscillator stage 3| remains ungrounded since contact 253 is unconnected. An electronic method is thus provided for disablingY the auto- .matic direction indicating action without the use .of radio frequency switching. The result is to :provide reception by the system as a radio receiver without any directional characteristics. With selective switch |00 in position 2, the pilot uses the system as a sensitive communication receiver or for radio beacon range reception.

VWitliselectol` switch |00 in position 3, the biasing .of modulator stage 86, 86 is returned to nor- .mal by short-circuiting resistor 9| through switch `blade b, properly biasing oscillator 92, 92 by connecting biasing resistance 94 to ground through switch blade a., normally grounding grid resistor |09. For automatic bi-directional operation, selector switch |00 is placed in position 3 in the modified arrangements of the unidirectional system shown in Figs. 3 and 4.

Fig. 3 is an electrical diagram illustrating the arrangement for` converting the automatic unidirectional radio indicator system of Figs. 1 and 2 to bi-directional operation for severe static conditions. Only a portion of the complete circuit is shown, it being understood that the remainder corresponds to that illustrated in Fig. 2. Other radio directional circuits may be used in practicing my invention. Broadly, the conversion from unidirectional to bi-directional reception in accordance with'the invention is accomplished by substituting a directional or loop antenna for the non-directional antenna, and simultaneously compensating for the difference in phase shift of their respective signal outputs. Switching means are employed to readily effect the couversion from the unidirectional to bi-directional r'eception, or vice versa.

The unidirectional system comprises rotatable loop antenna |0 secured to shaft within streamline housing |6','and non-directionalantenna 20 as described in conjunction with Figs. 1 and 2. Loop antenna l0 is connected to the primary of radio frequency transformer I6 through slip rings |2 and transmission cable I4. The circuit components of Fig. 3 bearingl the same numerals as corresponding components of Fig. 2 are identical. A four-pole double-throw switch operated by schematically indicated' rod 210 contains switch-arms or poles 21|, 212, 2.13, 214 operable in two positions. Position `4, marked Static A. D. F. refers to thecircuit conversion by four-pole switch 210 to automatic bi-directional operation for static reception con'- ditions. The conversion position' is accomplished by pressing button 215 of switch-rod' 210 as indicated by the arrow, which position thereof is as illustrated in Fig. 3. l

When switch 210 is moved to the conversion position, non-directional antenna 20; .normally connected to primary coil 2| of radio frequency antenna transformer, isY disconnected 'therefrom and connected to blank contact 216 by`arm21l. The auxiliary loop antenna |0a which is physically secured on rod with loop antenna'V I0, is electrically connectedto `auxiliary primary winding 2|a coupled with'secondary winding 24 of the radio frequency antenna transformer' by switch-arm 212 and contact 211, transmission cable 218 and slip rings 219. Switcharms-21| and 212 accordingly substitute auxiliary directional vantenna antenna 20 in coupling relationship with secondary Winding 24 of the antenna transformer.

Auxiliary antenna la is preferably arranged in '90 spaced relationship with respect to antenna I0. Thus when antenna I0 is in its minimum signal reception position, auxiliary antenna Illa is in its maximum signal reception position. A reference signal is thereupon impressed upon radio frequency amplier stage 8|) in a manner similar to that of non-directional antenna 20. Due to the characteristic of aloop antenna to substantially minimize static and parasitic signal reception in relation to the desired radio signal, as compared to reception by a non-directional antenna, a substantially improved signal-to-noise ratio is impressed upon radio frequency amplifier 80. Since loop antenna |0 is automatically kept in the null, signal position with respect to the received radio waves, auxiliarydirectional antenna |0a is correspondingly in the maximum signal reception position, and impresses a signal of substantial magnitude upon radio frequency amplifier 80. Intelligible aural reception is accordingly also afforded during even severe static conditions. l f

All the required signal components are thus present for the operation of the automatic directional system, and reliable and accurate automatic directional indication is afforded vi'n'ra manner similar to that described in connection with Figs. l and v2. In view of the bi-directional characteristic of .the auxiliary loop antenna |0a`,

tional antenna and a radio frequency amplier ulator stage to said radio frequency amplien coupled thereto, a directional antenna, va balanced modulator stage responsive to signals fnom said directional antenna, impedance means for biasing said modulator stage to substantially near `cut-off', means including circuit connections for coupling the output of said modulator stage to said radio frequency amplifier, means for selectively converting the system for operation on only one of said antennae comprising switchingV means including circuit connections for simultaneously short-circuiting the received non-directional signals and biasing said balanced modulator section to permit passage of the directional antenna signals through one-half thereof whereby operation on the directional antenna onlyis 3. In a radio'directional system, anon-directional antenna and a radio frequency amplifier coupled thereto, a rotatable directional antenna, a balanced modulator stage responsive to signals from said directional antenna, impedance 'means' for biasing said modulator stage' to substantially nearVcut-o, a control signal oscillator in` cir.

cuit, connection with said modulator stage to modulate radio frequency signals received. by said idirectional antenna, means including 'circuit connections for couplingv the output of said modulator stage :to said radio frequency'amplier, means' responsive tothe output of said radio frequency' amplifier for indicating the direction ofthe radio waves, and means for selectively converting vthe system for effectiveI operation on onlyone of said antennae comprising switching meansI including circuit connections for simultaneously grounding the received non-directional signals, rendering said'oscillator inoperative and unbalancing the biasing of said balanced modulator sectionto permit passage of the directionalantennav signals throughone-half thereof whereby" antenna only:i's" ef' operation on the directional fected. y ,.1

.4, In-aradio directional system,"a'non'direc'.

tionalantenna and a ra'dio'frequency.amplifier coupled y thereto, 'a vdirectional antenna, a'ibalanced modulator stage responsive to signalsy from said directional antenna; impedance means for'- biasing. .said modulator e stage' to substantially' near cut-"H, means' including circuit'connections for coupling the output of said modulator stage to said radio frequency amplifier, and means forselectively convertingA the system for operation ononly one of said antennae comprising switching `means ,including `circuit connections for simultaneously short-circuiting the non-direction-- al,.;antenna=signals' and biasing said balanced" modulator section to permit passage of the directional f antenna vsignals through fone-halt" thereof, whereby operation on the directional' antenna only lis effected, and alternatively forl overbiasingf-said balanced modulator to effectively suppress the directional antenna signals from the system for operation on only the non? directional antenna signals.

, 5. 'In vaY radio ydirectional system, a non-direc-'-k tional Aantenna and a radio frequency amplifier coupled thereto,Y a rotatable 1 directional antenna,"-

means responsive to thexoutput of said radio frequency amplifier for-indicating the direction of the radio waves,.a11d means for selectively conf. ver-ting the system for'operation on only one of said antennae 'comprising switching means vincluding circuit connectionsffor overbiasing rsaid balanced modulator and; 'rendering said oscillator inoperative to effectively .suppress the directional antennasig'nals in the .system-'for operation onl y on the non-directionalantenna signals. Y

6. Inzan automatic .radio 'directional system,`

anon-directional antenna and a' radio frequency amplifier .coupled thereto, :a rotatablel directional antenna, a'balanced modulatorv stage responsive to signalsfrom 'said directional antenna, irn-V pedance means'for biasing saidmodulator stage to substantially near 'cut-oma controlsignal oscillator in circuit connection with said modulator stage to modulatefradio frequency signalsv received by; said directional antenna,l means including circuitl connections for coupling the output of said. modulator stage to said radio vfrequency amplifier, means 4responsive to the output of saidradiolfrequency amplifier for rotating said directional antenna into the null signal reception'pos'ition', and means for selectively cone' vertingA the lsystem for operation on only one offsaid antennae comprising' switching` means including circuit connections for simultaneously grounding the received non-directional signals,

rendering" said Voscillator 'inoperative yand unbal- -non'directional4 antenna signals.

7. In a 'radio directional system, 'anondirecf tional antenna,"a1radio frequency amplifier coupled to-said nonedirectional antenna'a 'rotatable directional antenna, means responsive to signals from said directional antenna for modulating the directionaly signals with acontrol s'ignaL'mea-ns including circuit connections for' shiftingr the phase between thedirectional and non-directional signals by 90. forintroducing them k*to said radio'frequency amplifier'substantially Yin-phase said firstv mentionedrotatablev directional `an-y tenna, and. switching 'means4 including circuit connections?forsubstituting the coupling of' said non-directional antenna' with' said second directional antenna to' saidy radio yfrequencyv amplifier and rendering said phase shifting means ineffective whereby the'rsignal'channels of both of.` said directional antennae 'areplaced substan` tially' in-phas'e or '180 'out-of-phase relation at` said' radio' frequency amplifier vand* bidirectional bearings are effected by said 'directional ran-` tennae on the radio transrnittenr i 8. In a`ra'dio"dire'ctional system, a non-directionalfant'ennafa radio frequency amplifier' cou- A pled to saidnon-directional` antenna, a'drec'f tional'` antenna', means responsiveto signals 'from I said directional antenna for modulating the directional signals with a control signal, means including circuit connections for shifting the 180 out-ofsphaserelation, asecond directional antenna mounted withisaidrfirsi'.A mentioned'die' rectional antenna, 'andswitching means includ-f ing circuit `connections 'forl substituting the con# plingof saidnon+directio`nal antenna with-.said seconddirectional anternia-toesaidA radio' fre-f fluency amplifier; and 'renderingfs'aid phase Lshlt.

ing means ineffective wherebyltheflsignal channels of: b'othof said directional" antennae.' are placed.v substantially in-pha'se: 012;;180"l ,Zout-ofphasev relation *at* -saidradio frequency amplifier and iii-.directional bearings are Yeffected byrsaid directionall antennae :on theradio f i `9. In a radiozdirectionalsystem, a non-directional antenna, a firstradio frequency amplifier coupled to said non-directionall antenna, a rotatabledirectional antenna,y asecond radio fre# quency amplier coupled tosaid directionalA antenna, means responsive to `Athe output ofl said. second radio frequency amplifier for modulating the directional signal output thereflwith a con-` trolrsignal, means including circuit 4connections tion, a `second directional antenna,- Inounted with said first mentioned rotatable directional antenna in a v90 angolarirelationship;l andswitchmg means including circuit `connections for substi-A tuting the coupling of said non-directional antenna with saidsecond directional antenna to` said first radio frequency amplifierv and simul` taneously rendering `said 90 phaseshifting' means* ineffective whereby the signal :channels-of'both of said ldirectional antennae are placed substantially in'phase orrl80 out/-oi-phase. relationat` said first radio frequencyY amplifier. and bi-direc-f tional'bearings are effected by said directionah antennae on the radiotransmitter.V f

10. In a radio directional system, a non-direc.- tional antenna and a radiov frequency amplifier" coupled theretoga rotatable directional antenna,

a balanced modulator'- stage responsive tri/signals. from said directional antennaimpedance means for biasing said modulator gstage'toll substantially. neary cut-off; 4a control .signaloscillator in'cir-f cuit connection: with 'said modulator stage' to' modulate radio frequency signalsrecei'ved bysaid= directional antenna, means-including circuitxcons nections for coupling the 4output of said ,modulator stage to said' radio: frequency amplierfor indicating the direction'of the radio waves, means for selectively converting thel system: foreifec-v tive operation on only one ofy said antennae com# prising `switching means including'` circuit con-"f nections forsimultaneously grounding the re' ceived non-directional signals, rendering lsaid oscillator inoperative and unbalancing'the bias-f ing of said balanced modulator section to permit passage of the directional antenna Ysignals through one-halbthereoffwhereby operation on;

the directional antenna only is` effected, v and manuallyoperable-means including a switch nor` mally biased to an, open position effective, when operated while the system is-so converted, to ren-f phasel between the directionaleand non-direc-.f tional v:signals for :introducing them to said radio i frequency amplifier substantially iii-phase 1 or` derilsaid oscillator, operative to effectautoxatic direction. indication.-

1 4 Y Jill. In anV automatic radio directional system-1 a non-directional antennaand a radio .frequency z amplifier coupled thereto, a rotatable directional antenna, abalanced modulator stage nesponsivea torsignals from: said directional antenna, impedance-means for biasing said modulatorstageto substantially'near vcut-off, a control sigr1:z,llosci.l l latorin -circuitf connect-ion with said modulator'- stage touV modulate. 'radio frequency :signals re'- ceivedby said directionalantennapmea'ns ins cludi'ng circuit connectionsfor coupling theout-'f puti of said v modulator'stage to-saidradio foei-' quency amplifier,- means responsive tothel out-j put'of -said radio frequency amplifier forrrotating said directional antenna into the nullsig-y nal reception position,means for selectlvely'converting the system for' operation on only one of saidantennae comprising switching means irrcluding circuit connections for simultaneously; grounding the received non-directional signals, rendering said oscillator inoperative and/unbalancing .the biasingY of saidl balanced modulator: sectionto permit passage'of'the directional antenna signals throu'ghonehalf thereof whereby operation' on theA directional antenna effected and for overbiasing said balancedmodib" lator wand rendering saidv oscillator inoperative toi'eifectivelv suppressthe directional. antenna.'l signals in the system for operation only on the non-directional antenna. signals, 'and' operable vmeans, :including a switch normally biasedv to. an open position effective, when oper-1 ated while thesystem is so converted, to rende!" said: oscillator 'operative to effect automatic 0peration 'of such irectional antenna rotating means,"l I ,v .L i .12. In a radio directional system, a non-direc-'- tional antenna, a 'first radio frequency amplifier coupled to said non-'directional antenna; aro-J tatable directional antenna, a. second radiofrequency amplifier coupled to said directional a'nf tenne-Ineens responsive 'to the output 'ofsaid second radio frequency amplifier forfmdlat* ing the directional signal output lthelreoflwith a control signal, means including clrcuit=-conniecr tions interposed between said directional an;E tennaand'said second'amplifler for shiftlng'the'f phase of the=directional signals by 90 foriintroi' ducing them vto said rstfradio'frequency" "ami-V plifler substantially'- in-phase or 180"` 1 outolphase-relation; means responsive to the output ofsaid first radio frequency amplifier including' said control signal for' effecting unidirectional bearings on the radio' transmitter station, a sec'- ond directional antenna mounted with'said first mentioned rotatable directional ,antenna-in a'- 90 angular relationship,V 'and switching means' including circuit connections for substitutingthe coupling of v'said non-directional antenna with saidsecond directional'antenna to saidnrstra'- dio rfrequency amplifier and simultaneously bypassing said 90" phase shifting means and-said second amplier,...whereby the signal channels of both'of saiddirectional'antennae are placed'substantially lnephase'or'l" out-of-phase relation' at said first radio frequency amplifier andbi-y directional bearings vareeffected by said tlirecffk tonalfantennae'on'the radio transmitter. i

WILUAM PgLEARJ f 

